The following relates to the electric power arts, electric power grid management arts, and related arts.
Power outages are an unfortunate reality with any electrical power grid. Such outages can have myriad causes, such as downed overhead lines, blown transformers, generator failures, and so forth. Due to the interconnectedness of the electrical power grid, these problems can cascade as an initial failure produces an overvoltage or overcurrent condition that leads to further failures. Cascading is ultimately arrested by various automatic circuit isolation mechanisms built into the electrical power grid.
A power outage can last anywhere from a few seconds or less, up to several days or longer. A short power outage is often corrected by automatic electric power grid recovery mechanisms, such as operating automatic switches to bypass a blown transformer or downed transmission line, and in this case the power outage usually has limited adverse effects (e.g. resetting some electric clocks to “12:00 am”, or shutting off computers that do not include a battery backup).
Longer power outages are more problematic. The usually require human intervention to restore power. Additionally, a longer power outage adversely impacts loads that convert and store electrical energy in another form. Some examples of residential electric loads that store energy include: electric water heaters which store thermal energy in the form of heated water, heating, air conditioning, and ventilation (HVAC) systems which store energy in the form of a maintained temperature differential; refrigerators which also store energy as a maintained temperature differential; and electric vehicle charging stations which store electrochemical energy in a vehicle battery.
In response to a longer power outage, powerline technicians track down the cause of the power outage and take action to restore power. This is done as expeditiously as possible while maintaining technician safety. Conventionally, when power is restored on a given grid circuit, the restored power is delivered essentially instantaneously to all loads powered by that grid circuit. If those loads include energy storing loads (e.g. electric water heaters, HVAC, refrigerators, vehicle charging stations) then these loads often initially draw maximum power as they recharge, because during the extended power outage their supply of stored energy has typically been depleted. This simultaneous power draw can overload of the newly restored grid circuit causing a new power outage. Even if no new power outage is produced, the high initial power draw stresses the circuit which over time can lead to premature equipment failures.
Electrical power utilities, cognizant of this “cold load pickup” issue, sometimes restore power on a sub-circuit by sub-circuit basis in order to limit the power surges due to restarting energy storage loads. This is a variant on the “rolling blackout” concept. This approach is not targeted to particular types of loads, much less to particular individual loads, negatively impacts electrical customers, and can delay the total time to recover from an extended power outage.
The conventional “simultaneous startup” or “rolling startup” processes are a consequence of the conventional electric power grid delivery paradigm which is load-driven. As opposed to these load-driven approaches, in “demand response” approaches the electrical power demand is adjusted to better match available electrical power supply. Some simple demand response approaches rely upon incentivizing electrical power customers to operate their devices at times of off-peak demand, for example by pricing electrical power lower during off-peak hours.
More automated demand response techniques are being developed, in which the electrical supplier (e.g. the power company or other grid operator) can remotely control certain electric loads to operate during off-peak hours. In frequency control techniques, automated demand response is extended toward shorter time frames (e.g. on the order of minutes or seconds) to enable load power cycling to compensate for short-term loading changes that are reflected in changes to the instantaneous electrical frequency on the electric power grid.
Energy storage loads (e.g. electric water heaters, HVAC, refrigerators, vehicle charging stations) are particularly valuable as controlled loads for demand response systems because the stored energy provides flexibility as to when these loads operate. For example, an electric water heater typically has a “dead band” temperature range around its set point temperature, and conventionally the heater elements are shut off when the temperature exceeds the top of the dead band and are turned on when the temperature falls below the bottom of the dead band. Most of the time the temperature is within the dead band, and in this state the heater elements may be turned on or off for a secondary purpose such as frequency control, so long as the power cycling does not cause the temperature to move outside of the dead band.
In a demand response system, it is possible to leverage the remote control of specific loads, and especially of energy storage loads, to provide targeted startup of energy storage loads. In some approaches, load restart is staggered, similarly to the “rolling start-up” approach but more targeted to energy storage loads using the automated demand response infrastructure. In another approach, energy storage loads are restarted by the demand response infrastructure using some reduced power level.
While these approaches have numerous advantages, they also have substantial practical barriers to widespread implementation. They are predicated upon availability of sufficient communication infrastructure to allow the grid operator to perform individualized, targeted load startup. Such advanced communication infrastructure is not yet widely available, especially in residential areas where demand response may be economically impractical. For example, it may not be cost effective to provide individualized communication between the grid operator and each of several hundred thousand residential water heaters in a large city. Even if installed, this communication infrastructure may become unavailable at the critical time as the power outage may cause loss of electrical power to the communication system.